3s–3p laser gain and x-ray line ratios for the carbon isoelectronic sequence

Abstract

The populations of the 46 levels belonging to the configurations 2s22p2, 2s2p3, 2p4, 2s22p3s, 2s22p3p, and 2s22p3d have been calculated for ions in the C I isoelectronic sequence with atomic numbers Z=18, 22, 26, 30, 34, and 36 and for electron densities from 1015 to 1022 cm−3. The populations of the 2s22p3p levels are relatively large owing to the large electron collisional monopole excitation rates from the ground configuration and to the small radiative decay rates to the ground configuration. This results in population inversions for transitions of the type 3s–3p. The gain coefficients for these transitions are determined and are compared to previous calculations. At high electron densities where collisional mixing of the excited levels becomes important, the intensities of the x-ray transitions from the 2s22p3p levels to the 2s2p3 levels decrease relative to the x-ray transitions from the 2s22p3s and 2s22p3d levels. The density dependence of these x-ray line ratios is also presented. These line ratios represent a promising diagnostic for electron density.